Process for preparing isocoumarins

ABSTRACT

The present invention provides a process from preparing isocoumarin-3-yl derivatives comprising reacting a homophthalic anhydride derivative with a carbonyl compound, wherein the carbonyl group is substituted with an acyl activating group, in the presence of a reaction medium comprising a solvent and a base. The invention also encompasses a process for the preparation of homophthalate esters useful in the preparation of homophthalic anhydride reactants as well as an integrated process wherein the twp reactions are carried out sequentially to afford the desired isocoumarin derivative.

This application claims priority to U.S. Application serial No.60/303,532, filed Jul. 6, 2001 and to U.S. Application serial No.60/352,407, filed Jan. 28, 2002.

FIELD OF THE INVENTION

The present invention relates generally to the chemical preparation ofisocoumarin compounds. More specifically, the invention relates to theconversion of homophthalic anhydrides to isocoumarins and thepreparation of homophthalic acid intermediates. Isocoumarin derivativesare valuable compounds in the fields of angiogenesis inhibition,immuno-regulation, and cancer therapy.

BACKGROUND OF THE INVENTION

Isocoumarins have been synthesized by a number of different methods.These methodologies include, but are not limited to: oxidation ofindenes, indanone and indenones; condensation via Stobbe condensationwith aldehydes and ketones and Claisen condensation with formates andoxalates; cyclization of 2-carboxybenzyl ketones, 2-vinylbenzoic acids,α-cyanohomophthalic acids and 2-formylbenzoates; and reduction ofphthalides. For reviews of isocoumarin synthesis, see Barry, ChemicalRev. 64:229-260, 1964; Napolitano, Org. Prep. Proced. Int. 29:631-664,1997.

Homophthalic anhydrides have also been utilized in the synthesis ofisocoumarin derivatives. 2-Carboxyphenylacetates can be prepared bymethanolysis of homophthalic anhydrides. Lithium borohydride reductionof these half-esters yields 3,4-dihydroisocoumarins. (Bose & Chaudhury,Tetrahedron. 20:49-51, 1964). Condensation of homophthalic anhydridewith hydroquinone in the presence of stanic chloride yields2-(2,5-dihydroxyphenyl) isocoumarin (Sorrie & Thomson, J. Chem. Soc.2244, 1955). Homophthalic anhydride adds to ferrocene to produceferrocenylhomophthalic acid, which can be cyclized to3-ferrocenylisocoumarin (Boichard, Compt. Rend. 253:2702, 1961).Further, Perkin condensation of homophthalic anhydrides with aromaticaldehydes in the presence of bases such as triphenylmethylsodium, yields3-phenyl-3,4-dihydroisocoumarin-4-carboxylic acids (Jones & Pinder, J.Chem. Soc., 2612, 1958).

Methods for preparing isocoumarin-3-yl acetic acid derivatives aredisclosed in WO0107429. In one process, a homophthalate monoesterderivative is reacted with a malonic acid monoester salt in a suitablesolvent in the presence of a condensing agent to form a β-oxocarboxylicacid derivative, which is subsequently cyclized in a suitable inertsolvent, in the presence of a base. The reaction is as follows:

An alternative method of preparation of the same compound disclosed thereaction of a homophthalic acid derivative with a malonyl halidemonoester in the presence of a base. One disadvantage of these methodsis that the synthesis disclosed in WO0107429 for homophthalate estershas a low yield and provides an intermediate ester with free hydroxygroups that must be subsequently protected in a separate step.

The synthesis of 3-yl-isocoumarins is also disclosed by Tirodkar &Usgaonkar, J. Indian Chem Soc., 46, 1934-933, 1969; Tirodkar &Usgaonkar, Indian J. Chem, 9: 123-125, 1970; Tirodkar & Usgaonkar, J.Indian Chem Soc., 48:192-198, 1971; and Sinha et al, Indian J.Heterocyclic Chem., 1:235-240, 1992. These methods describe theformation of 4-carboxy-3-yl-isocoumarins by reaction of an anhydridewith an isochroman-1,3-dione carbanion or enolate intermediate, formedfrom the corresponding homophthalate under basic conditions.Decarboxylation under acidic conditions or by heating resulted in thecorresponding 3-yl-isocoumarin. This reaction is summarized in FIG. 1.

Despite the preparative methods for isocoumarins known in the art, thereis still a need for economically preferable, effective and efficientprocess for the preparation of isocoumarin derivatives. The object ofthe present invention is to provide such a process. Further objects areto minimize the number of process reaction steps, to enhance overallyields of desired end products and to provide a process that is readilyscalable for the production of commercial-scale quantities. Otherobjects and advantages will become apparent to persons skilled in theart and familiar with the background references from a careful readingof this specification.

SUMMARY OF THE INVENTION

In its most general terms, the present invention provides for thepreparation of isocoumarin derivatives and intermediates useful in suchpreparative procedures. One aspect of the invention provides a processfor preparing isocoumarin derivatives comprising reacting a homophthalicanhydride derivative with a carbonyl compound, wherein the carbonylgroup is substituted with an acyl activating group, in the presence of areaction medium comprising an inert solvent and a base. The inventorsdiscovered this novel reaction results in the formation of isocoumarinderivatives in high yield and provides an efficient method ofpreparation of such compounds. Another aspect of the present inventionis the preparation of homophthalate esters based on the discovery that,surprisingly, the addition of a malonate anion to a benzyne intermediateformed from a 2,4-disubtituted halobenzene, results in the selectiveproduction of a 3,5-disubstituted homophthalate ester. Such esters canbe readily converted into the equivalent anhydride and are, thereby,useful in the preparation of isocoumarin derivatives according to themethods provided by the present invention

In one aspect, the present invention provides a process for thepreparation of the isocoumarin derivatives of formula (1):

where R¹ and R² independently represent hydrogen, halogen, which may bechloro, bromo, iodo of fluoro, an aryl group, a heteroaryl group, or aC₁-C₆ alkyl, C₁-C₆ alkenyl, C₁-C₆ alkynyl, C₁-C₆ acyl, or C₁-C₆ alkoxygroup. R¹ and R² further independently represent the substituted aminofunction —NR⁴R⁵, where either R⁴ is hydrogen and R⁵ is sulfonyl or C₁-C₆acyl or where R⁴ and R⁵ are independently C₁-C₆ alkyl or C₁-C₆ acyl. Ina preferred embodiment, R¹ is hydrogen. In another preferred embodiment,R² is methyl.

R³ represents an electron withdrawing group. In preferred embodiments,R³ is an electron withdrawing group selected from aryl, hetroaryl,sulfonate, phosphonate, cyano, —CO₂R⁷, wherein R⁷ is C₁-C₆ alkyl, or anacid halide —COR⁸, wherein R⁸ is a halogen, which may be chloro, bromo,iodo of fluoro. In a more preferred embodiment, R³ is —CO₂C₂H₅. R³ mayalso form a ring structure with R², wherein the ring structureincorporates an electron withdrawing element, such ring structuresinclude anhydrides, lactones, oxo-cycloalkanes and cyclic amides,including lactams and lactims.

The substituents represented by X include halo, which may be fluoro,chloro, bromo or iodo, aryl, heteroaryl, C₁-C₆ alkyl, C₁-C₆ alkenyl,C₁-C₆ alkynyl, C₁-C₆ acyl, or C₁-C₆ alkoxyl, or —NR⁴R⁵, where R⁴ and R⁵are as defined above. X further represents —SO₂R⁶, where R⁶ is C₁-C₆alkyl or C₁-C₆ acyl. The subscript n is an integer from 0 to 4, with thecaveat that when n is 2, 3 or 4, the X substituents may be the same ordifferent. In a preferred embodiment, subscript n is 2 and X is the sameand is —OCH₃. In a more preferred embodiment, the isocoumarin derivativeis 2-(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-propionic acid ethyl ester(2)

The process comprises reacting a homophthalic anhydride of formula (3):

where R¹, X and subscript n are as defined above, with a carbonylcompound of formula (4):

where R² and R³ are as defined above, and Y is an acyl activatingsubstituent. In preferred embodiments, Y is a halogen, pyridyl oraryloxy, and more preferably imidazoyl or chloro.

The reaction medium further comprises an inert solvent and a base. Incertain embodiments, the solvent is an aprotic solvent such as ahalogenated or ethereal solvent. In a preferred embodiment, the solventis acetonitrile or N-methyl pyrrolidinone. In some embodiments of thepresent invention, the base can be a tertiary amine, amidine, amide or atertiary alkoxide base. In preferred embodiments, the base istriethylamine, N,N-tetramethylguanidine or1,8-diazabicyclo[5.4.0]-undec-7-ene.

In some embodiments of the present invention,2-(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-propionic acid ethyl ester(2), undergoes hydrolysis to remove the ethyl ester group and the methylgroup at position 8 to produce2-(8-hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl)-propionic acid (5),also known as NM-3, which is disclosed and claimed in U.S. Pat. No.6,020,363, hereby incorporated by reference:

An alternative reaction to that with the carbonyl compound (4), iswherein the homophthalic anhydride (3) undergoes a self condensation toproduce the isocoumarin derivatives depicted by compound (6):

wherein R¹, X and n are as previously defined. The reaction is believedto proceed in a similar fashion to that of the compounds of formula (3)with the activated carbonyl compounds of formula (4). Thus, similarreactions conditions may be used to from the condensation products offormula (6).

Another aspect of the present invention is a process for the preparationof homophthalate derivatives of formula (7):

wherein W represents a carboxy protecting group, which in preferredembodiments is methyl or ethyl. R⁹ and R¹⁰ independently represent thesubstituents as described above for X. In preferred embodiments, R⁹ andR¹⁰ are independently C₁-C₆ alkyl or C₁-C₆ alkoxy. R¹ is as definedabove, and in a preferred embodiment is hydrogen.

The process comprises reacting a 2,4-disubstituted or a3,5-disubstituted halobenzene derivative of formula (8) or (9)respectively:

where R⁹ and R¹⁰ are as defined above, and R¹³ is a halogen, which, insome embodiments, is chloro, fluoro or bromo, a sulfonate ester or aleaving group such as tosylate or triflate; and a malonate ester offormula (10):

where W and R¹ are as defined above, and where in a preferredembodiment, R¹ is hydrogen, in the presence of a solvent and a strongbase, for example a base with a pKa in water of about 30 or above. In apreferred embodiment, the solvent is tetrahydrofuran. In other preferredembodiments, the strong base is lithium diisopropylamide (LDA), lithiumtetramethylpiperidide, lithium hydride or a mixture of bases such as LDAand sodium hydride or potassium hydride. In other preferred embodiments,R¹³ is chloro or bromo.

In some embodiments, the malonate ester (10) is first reacted with astrong base to form a malonate ester salt (11):

wherein M⁺ is a monovalent cation. The base may be alkali metal base,which may be sodium hydride or lithium hydride, wherein M⁺ in themalonate salt (11) is Na⁺ and Li⁺ respectively. Either the2,4-disubstituted halobenzene (8) or 3,5-disubstituted halobenzene (9)is then added with the optional addition of a second strong base, theaddition of which can be either before or after the addition of thedisubtituted halobenzene. In a preferred embodiment, the optional secondstrong base is added after the disubtituted halobenzene (8) or (9). Inanother preferred embodiment, the optional second strong base is LDA.

The process according to the present invention is highly selective inthat the desired homophthalate derivative of formula (7) is produced ina molar ratio of at least about 7.0:3.0, or in a molar ratio of at leastabout 8.0:2.0, or in a molar ratio of at least about 9.0:1.0 incomparison to the homophthalate derivative of formula (12). In apreferred embodiment, the desired homophthalate (7) is producedsubstantially free of the positional isomer (12), that is, in a molarratio of at least about 9.5:0.5 of (7):(12). In another preferredembodiment, there is no detectable level of the homophthalate derivativeof formula (12) produced during the reaction of a disubstitutedhalobenzene derivative of formula (8) or formula (9) and a malonateester of formula (10), as measured by HPLC and U.V. analyses.

The process further comprises embodiments wherein the carboxy protectinggroups W are removed to form the homophthalic acid derivative of formula(13):

In some embodiments, the homophthalic acids of formula (13) undergodehydration to form the homophthalic anhydrides of formula (14):

wherein R¹, R⁹ and R¹⁰ are as defined above.

The process of the invention also further comprises reacting theanhydride of formula (14) with a carbonyl compound of formula (4),wherein the reaction medium comprises a solvent and a base to afford thederivatized isocoumarin product. In some embodiments, the carbonylcompound of formula (4) is the carbonyl compound of formula (15):

wherein R¹¹ and R¹² are independently C₁-C₆ alkyl, and Y is an acylactivating group. In a preferred embodiment, the reaction of theanhydride of formula (14) wherein R¹ is hydrogen, with the carbonylcompound of formula (15) results in the formation of the isocoumarinderivative of formula (16):

In a preferred embodiment, where R⁹ and R¹⁰ are methoxy, R¹¹ is methyland R¹² is ethyl, the reaction process of the present invention providesthe isocoumarin derivative2-(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-propionic acid ethyl ester(2). In another preferred embodiment, the process further comprisesremoval of the ethyl ester group and the methyl group at position 8 of2-(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-propionic acid ethyl ester(2) to provide2-(8-hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl)-propionic acid (5).

Also within the scope of the invention is an integrated stepwise processwherein isocoumarins of formula (1) are prepared starting from asubstituted halo-benzene of formula (8) or formula (9) which is reactedwith a malonate ester of formula (10) to afford a homophthalatederivative of formula (7), which in turn, after optionaldeprotection/dehydrations, is reacted with a carbonyl compound offormula (4) to afford the desired isocoumarin derivatives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Summary of isocoumarin syntheses as per Tirodkar & Usgaonkar, J.Indian Chem Soc., 46, 1934-933, 1969; Tirodkar & Usgaonkar, Indian J.Chem, 9: 123-125 1970; Tirodkar & Usgaonkar, J. Indian Chem Soc.,48:192-198, 1971; and Sinha et al, Indian J. Heterocyclic Chem.,1:235-240, 1992. R is H or methoxy and R′ is alkyl or aryl.

FIG. 2: Summary of proposed mechanism of reaction of the presentinvention.

FIG. 3: Summary of the synthesis of 2-carboxy-3,5-dimethoxy benzoicacid.

DETAILED DESCRIPTION OF THE INVENTION

1. Preparation of Isocoumarins from Homophthalate Anhydride Derivatives

The present invention provides a process for preparing isocoumarincompounds by using a homophthalate anhydride as the nucleophiliccomponent in a reaction with a suitable electrophile. Thus the reactioncan be depicted as follows, wherein all substituents are as previouslydefined:

Without being bound by any particular theory, it is presently believedthat the mechanism for the reaction of the present invention is shown inFIG. 2. The initial acylation forms the novel compound (17) whichrearranges to the dioxabicyclo[2,2,2]-octene skeleton of compound (18).The ortho ester function then opens under basic conditions to givecompound (19), which readily decarboxylates. The resulting extendedenolate is then thermodynamically protonated at the exocylic methanecarbon to afford the isocoumarin compound (1).

The molar ratio of compound (4) to (3) to be reacted is not consideredto be critical and is preferably in the range of about 1.0 to about 1.5.The molar ratio of base to other reactants is also not critical, andtypical molar ratios of base to the homophthalic anhydride of formula(3) are in the range of about 1.0 to about 1.5. and are preferably about1.0 to about 1.2.

The Y substituent is an acyl activating group. The term “acyl activatinggroup” refers to a substituent to a carbonyl that promotes nucleophilicaddition reactions to the carbonyl. Suitable activating substituents arethose which have a net electron withdrawing effect on the carbonyl. Forexample, a halogen attached to carbonyl (i.e., acyl halides) activatesthe carbonyl for nucleophilic addition. Suitable halogens includechloro, bromo, or iodo. Other typical electron withdrawing groupsinclude groups that when combined with the carbonyl form an ester oramide. Such groups include hydroxybenzotriazole, imidazole, anitrophenol, including 4-nitrophenoxy and 2-nitrophenoxy,pentachlorophenoxy, pentafluorophenoxy, N-hydroxysuccinimide,dicyclohexylcarbodiimide, N-hydroxy-N-methoxyamine,3-hydroxy-3,4-dihydro-4-oxo-benztriazine, 1-hydroxybenztriazole,1-hydroxy-7-aza-benzotriazole, aryloxy, pyridyl, and the like. Otheracyl-activating groups include acyloxy, acylisourea and acylazide.

The R³ substituent is an electron withdrawing group, which thus alsoencompasses the compounds represented by the Y substituent. The R³substituent may be an aryl or heteroaryl group, wherein the electronwithdrawing properties of the group may be due to the inductive effectof the aryl or heteroaryl ring system and/or by substituents if present.R³ may also form a ring structure with R², wherein the ring structureincorporates an electron withdrawing element. Examples includeanhydrides, such as when the ring formed by linking R³ and R² isequivalent to glutaric anhydride or succinic anhdride, lactones,oxo-cylcoalkanes, such as oxo-pentane, oxo-cyclohexane,oxo-cycloheptane, and oxo-cyclooctane, preferably when the carbon withthe oxo-substituent is beta to isocoumarin nucleus, and cyclic amides,such as lactams and lactims. Wherein R³ is a phosphonate, the termphosphonate encompasses the free acid and esters, such esters to includealkyl esters, e.g., methyl, ethyl, n-propyl, isopropyl and t-butylesters.

When used herein, the term alkyl, alkenyl, alkynyl, acyl and alkoxyinclude halogenated alkyl, alkenyl, alkynyl, acyl and alkoxy groups.Such halogenated groups to include fluoro alkyl, alkenyl, alkynyl, acyland alkoxy groups, wherein the degree of fluoro substitution ranges fromone fluoro to perfluoro alkyl, alkenyl, alkynyl, acyl and alkoxy groups.

When used herein, the term “aryl” refers to an unsaturated aromaticcarbocyclic group of from 6 to 14 carbon atoms having a single ring(e.g., phenyl) or multiple condensed rings (e.g., naphthyl or anthryl).The aryl groups may be optionally substituted, wherein such substituentsinclude halo, akyl, akenyl, alkoxy, acyl, acylamino, acyloxy, amidino,amino, nitro, aryl or heteroaryl.

When used herein the term “heteroaryl” refers to, unless otherwisedefined, a single or a fused ring containing up to four heteroatoms ineach ring, each of which is selected from oxygen, nitrogen and sulphur,which rings, may be unsubstituted or substituted by, for example, up tofour substituents. Each ring suitably has from 4 to 7, preferably 5 or 6ring atoms. A fused ring system may include carbocyclic rings and needinclude only one heteroaryl ring.

Representative examples of heteroaryl groups include pyridyl, pyrimidyl,pyrazinyl, pyridazinyl, thiaphene, thiazolyl, thiadiazolyl,benzothiazolyl, isoxazolyl, pyrazolyl, triazinyl, and imidazolyl whichmay be unsubstituted or substituted by up to four substituents (forpyridyl and benzothiazolyl), three substituents (thiophene, pyrimidyl,pyrazinyl, pyridazinyl, pyrazolyl), two substituents (thiazolyl,isoxazolyl, triazinyl and imidazolyl) or one substituent (thiadiazolyl)which may be the same or different and include halo, haloalkyl, akyl,akenyl, alkoxy, acyl, acylamino, acyloxy, amidino, amino, nitro, aryl orheteroaryl.

In one aspect of the invention, the solvent used in the reaction mixtureis an aprotic solvent, which is a solvent that neither yields noraccepts a proton. Aprotic solvents include non-halogenated andhalogenated aromatic and aliphatic hydrocarbons, such as xylenes,toluene, dichloromethane and the like. Aprotic solvents also includeethereal solvents such as tetrahydrofuran, and further include tertiaryamines, pyridine and hindered pyridines such as lutidine, collidine, andpicoline. Other aprotic solvents include, but are not limited to,acetonitrile, propylene carbonate, sulfolane (tetramethylene sulfone),N,N-dimethylformamide, N,N-dimethyacetmide, N-methylpyrollidone,dimethylsulfone, dimethylsulfoxide, triglyme (triethylene glycoldimethyl ether), N-methylpyrrolidinone, benzonitrile,hexamethylphosphoramide, toluene, dioxane or mixtures of two or more ofsuch materials.

Various bases may be used in the present invention, including amidinebases such as 1,5-diazabicyclo[4.3.0]-non-5-ene or1,8-diazabicyclo[5.4.0]undec-7-ene. Other bases include organic aminebase like triethylamine, diethylamine, diethyl isopropylamine, DABCO orrelated di- or trialkylamines. Tertiary alkoxide bases include alkalinemetal alkoxides such as the potassium, sodium and lithium salts oftert-butoxide and tertamylate. Hindered bases include bases such aslithium diisopropylamide, lithium bis(trimethylsilyl)amide, lithiumtetramethylpiperidide, lithium, sodium or potassiumhexamethyldisilazide, N,N,N′,N′-tetramethylguanidine (TMG) and the like.When the Y substituent of compound (4) is a halide, it is preferred touse a strong base with a pKa in the range of 11-13.6, such basesincluding DBU and TMG, optionally in combination with a weaker base suchas triethylamine (“TEA”). In some embodiments, the strong base is addedto the anhydride (3) with the subsequent addition of compound (4)wherein Y is a halide, with a second base. In a preferred embodiment,the second base is triethylamine. Use of TMG requires that the tertiaryamine base is added prior to the addition of the acyl chloride preventacylation of the TMG.

In typical embodiments, the reaction is suitably conducted at atemperature of about room temperature or at a temperature up to theboiling point of the reaction solvent mixture wherein the reactionmixture is refluxed. Such temperatures employed may be about 20° C., orabout 30° C., or about 40° C., or about 50° C., or about 60° C., orabout 70° C.

The preferred order and manner of addition for any specific embodimentcan be determined by routine experimentation with a view towards bothreaction performance and chemical engineering and productionconsiderations. In a preferred embodiment, the anhydride (3) is addedslowly to the reaction mixture.

The present invention also encompasses the removal of hydroxyl andcarboxyl protection groups when desirable from isocoumarin derivativesencompassed by formula (1). For example, the methyl group from the8-methoxy substituent may be removed from2-(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-propionic acid ethyl ester(2), as disclosed in WO0107429, hereby incorporated by reference.Deprotecting the 8-position can be achieved by use of an alkaline metaliodide (e.g., potassium or sodium iodide) and a magnesium halide,preferably magnesium chloride, in an inert solvent (e.g.,tetrahydrofuran, dioxane or acetonitrile) at 20 to 100° C., andpreferably 60 to 80° C. Subsequent removal of the ethyl ester functionof the 8-hydroxy derivative of the compound of formula (2), therebyproducing 2-(8-hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl)-propionicacid (5), can be achieved by hydrolytic reactions well known in the art.Removal of protecting groups from other isocoumarin compounds of thepresent invention can be achieved by routine experimentation utilizingmethodologies and procedures know in the art.

2. Preparation of 3,5-Dialkoxy Substituted Homophthalates andCorresponding Anhydrides

Homophthalate anhydrides as represented by formula (3), used in thepresent invention for the preparation of isocoumarin derivates, aresuitably prepared from the corresponding homophthalic acid derivatives(20):

Wherein X_(n) and R¹ are as previously defined and W represents acarboxyl protecting group. The homophthalic acid derivatives of formula(20) can be prepared by several methods. WO0107429, herein incorporatedby reference, discloses the preparation of 3,5-disubstituedhomophthalates by reacting an acetonedicarboxylic acid ester with adiketene. Other methods include cycloaddition of allenyl esters todienes (Tamura et al., Chem. Pharm. Bull. 32:3259-3262, 1984; Roush etal., J. Org. Chem. 57:6622-6629, 1992; Langer et al., Tetrahedron Lett.41:4545-4547, 2000, all herein incorporated by reference) andortho-lithiation of benzoic acid derivatives (Cushman and Dekow,Tetrahedron 34:1435-1439, 1978; DeSilva et al., Can. J. Chem.57:1598-1605, 1979; Tamura et al., Tetrahedron 40:4539-4548, 1984, allherein incorporated by reference). A further method is the addition ofmalonate anions of formula (22) to the benzynes of formula (21) (Shairet al, J. Am. Chem. Soc. 118:9509-9525, 1996; Kita et al., J. Am. Chem.Soc. 123, 3214-3222, 2001, both herein incorporated by reference). Thelatter method results in the two isomers of formulas (20) and (23):

One aspect of the present invention encompasses the utilization of thismethod in the surprising selective production of a 3,5-dialkoxysubstituted homophthalate isomer. The product ester is believed to arisethrough a benzyne intermediate that is formed in situ. In this aspect ofthe invention, the benzyne intermediate is formed by reaction of astrong base, for example a base with a pKa in water of about 30 orabove, with a 2,4-substituted or 3,5-disubstituted halobenzene offormulas (8) and (9) respectively:

wherein R⁹ and R¹⁰ are as defined above and R¹³ is a halogen, which maybe bromo, chloro, iodo or fluoro, or a sulfonate ester or a leavinggroup such as tosylate or triflate. Examples of suitable strong basesare lithium, sodium and potassium hydrides and lithium, sodium andpotassium secondary amides. The secondary amine may be a dialkylamide,e.g., diethylamide, diisopropylamide, ditertiarybutylamide,dicyclohexylamide, t-butyl-cyclohexylamide, N-t-amyl-N-t-butylamide,N-isopropyl-N-cyclohexylamide orN-(1′-ethylcyclohexyl)-1,1,3,3-tetramethylbutylamide or a cycliccompound, e.g., piperidine or 2,2,6,6-tetramethylpiperidine. Inpreferred embodiments the strong base is lithium diisopropylamide,lithium tetramethylpiperidide, lithium hydride or sodium hydride. Suchstrong bases may also be formed in situ by addition, typically at lowtemperature such as −60° C. to −70° C., of n-butyl lithium and therespective free bases, e.g., diisopropylamine or tetramethylpiperidinein a suitable solvent. In a preferred embodiment, the solvent istetrahydrofuran. Other solvents may include 2-methyltetrahydrofuran,diethylether, diisopropylether, tert-butylmethyl ether, dioxane, orhexanes. In another embodiment the base is a hydride, such as potassiumor sodium hydride, wherein a cation complexing agent such as1,4,7,10,13,16-hexaocyclooctadecane (“18-crown-6”) or other crown ethermay optionally be added. The formation of benzyne intermediates byinteracting aryl halides with strong bases is disclosed in U.S. Pat. No.4,296,029 and Shair et al, J. Am. Chem Soc. 118:9509-9522, 1996, bothherein incorporated by reference.

The benzyne intermediate thus formed reacts with a malonate ester anionof formula (22), wherein W represents a carboxy protecting group. Thisreaction typically proceeds a low temperature, which may be about 10° C.to about −80° C., and may be about 5° C., about −10° C., or about −20°C., or about −30° C., or about −40° C. In some embodiments of thepresent invention, higher temperatures, including room temperature, areused. In some embodiments the malonate anion is first formed by reactingthe malonate ester (10) with a strong base to form the malonate salt(11). Suitable strong bases include alkali metal bases, for examplelithium, sodium and potassium hydride and strong amide bases such as LDAand lithium 2,2,6,6-tetramethylpiperidiide (LiTMP). The 2,4-substitutedhalobenzene (8) or 3,5-disubstituted halobenzene (9) is then added tothe reaction. An optional second strong base may also be added before orafter the halobenze (8) or (9). A preferred optional strong base is LDA.A preferred method is to add the second optional strong base slowlyafter the halobenze (8) or (9), thereby slowly forming the benzeneintermediate.

As used herein, the term “carboxy protecting group” refers to acarboxylic acid protecting ester group employed to block or protect thecarboxylic acid functionality while the reactions involving otherfunctional sites of the compound are carried out. Examples of carboxyprotecting groups include straight or branched chain (C₁₋₁₂)alkyl groups(e.g., methyl, isopropyl, t-butyl); lower alkoxy lower alkyl groups(e.g., methoxymethyl, ethoxymethyl, isobutoxymethyl); lower aliphaticacyloxy lower alkyl groups (e.g. acetoxymethyl, propionyloxymethyl,butyryloxymethyl, pivaloyloxymethyl); lower alkoxycarbonyloxy loweralkyl groups (e.g., 1-methoxycarbonyloxyethyl,1-ethoxycarbonyloxyethyl); aryl lower alkyl groups (e.g., benzyl,p-methoxybenzyl, o-nitrobenzyl, p-nitrobenzyl, benzhydryl andphthalidyl); tri(lower alkyl)silyl groups (e.g., trimethylsilyl andt-butyldimethylsilyl); tri(lower alkyl)silyl lower alkyl groups (e.g.,trimethylsilylethyl); and (C₂₋₆) alkenyl groups (e.g., allyl andvinylethyl). The species of carboxy-protecting group employed is notcritical so long as the derivatized carboxylic acid is stable to theconditions of subsequent reaction(s) and can be removed at theappropriate point without disrupting the remainder of the molecule.

Methods particularly appropriate for the removal of carboxyl protectinggroups are well known in the art and include for example acid-, base-and metal-catalyzed hydrolysis. Methods of dehydrating homophthalic acidderivatives to form anhydrides are known in the art and include use oftrimethylsilyl(ethoxy)acetylene (Kita et al., J Org. Chem., 51:4150-4158, 1986, herein incorporated by reference) and use of aceticanhydride, e.g., as exemplified in Example 5. The anhydrides thus formedby this aspect of the present invention, are useful as reactants in theaspect of present invention relating to the preparation of isocoumarinderivatives, as described above in Section 1.

EXAMPLES OF THE INVENTION

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The following specific examples are intended merelyto illustrate the invention and not to limit the scope of the disclosureor the scope of the claims in any way whatsoever.

Example 1 2-(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-propionic AcidEthyl Ester (2)

An oven dried, 25 mL, 3 neck flask, equipped with a magnetic stir barunder N₂ purge was charged with 0.200 g of ethyl-2-methyl malonate (24)at ambient temperature. Acetonitrile (“MeCN,” Aldrich, Milwaukee, Wis.),10 mL, was added via syringe over 1 minute to the stirring solidanhydride. Carbonyl diimidazole (“CDI,” Aldrich, Milwaukee, Wis.), 0.291g in 3 mL acetonitrile, was added via syringe over 10 minutes.Triethylamine (“TEA,” Aldrich, Milwaukee, Wis.), 0.25 mL, was added tothe solution over 30 sec. 6,8-Dimethoxy-isochroman-1,3-dione (25), 0.200g in 4 ml acetonitrile, was added via syringe over 15 minutes at ambienttemperature. The reaction mixture was stirred at ambient temperature for5 hours and several aliquots were taken for in-process controls. Sampleswere analyzed by reverse-phase HPLC using a C18 5μ column (Phenomenex)and a mobile phase of 1:1 acetonitrile and water at a flow rate of 1ml/min. Typical retention times are: imidazole (26) 2.3 min; anhydride(25) 4.4 min; dimer isocoumarin (27) 5.3 min; and isocoumarin (2) 7.5min. Quantification was by calculation of peak area of UV detection at244 nm. A byproduct, identified by NMR and mass spectrometry as theself-condensation product of the anhydride (27) was formed during thisreaction.

Consumption of the anhydride (25) and production of isocoumarin (2) anddimer (27) with time are shown in Table 1.

TABLE 1 Anhydride Isocoumarin Dimer Time (25) (2) (27) Start  0.0 hr90.6%  8.9%  0.5%  1.0 hr 70.8% 19.9%  9.3%  2.5 hr 54.0% 28.8% 17.2% 4.0 hr 11.4% 72.5% 16.1%  5.0 hr 10.0% 74.6% 15.3% End 21.5 hr  2.0%80.1% 17.9%

The solution was warmed in oil bath at between 50-60° C. for about 3.5hr. Analyses of an in-process control aliquant taken at end of the timeperiod indicated 89.0% isocoumarin (2) and 11.0% dimer (27). The solventwas removed on a rotary evaporator to give an orange oil. The crude oilwas dissolved in ethyl acetate. The solution was washed with 1N HCl andthe wet organic layer was dried over MgSO₄. The solvent was removed invacuo. NMR revealed presence of dimer (27) byproduct. The crude oil wasredissolved in ethyl acetate (10 ml) and the solution was washed twicewith sat. NaHCO₃ (3 ml). The solution was dried over MgSO₄ and solventremoved to give isocoumarin (2) as an orange oil. NMR analysis indicatedno detectable level of dimer (27). Crystals of isocoumarin (2) formed onstanding. Designations assigned to NMR analysis of the isocoumarin offormula (2) are as follows:

Proton a, 6.45 ppm (doublet, J=2.3 Hz, 1H); proton b, 6.37 ppm (doublet,J=2.3 Hz, 1H); proton c, 6.25 ppm (singlet, 2H); proton d, 4.18 ppm(quartet, J=7.2 Hz, 2H); proton e, 3.96 ppm (singlet, 3H); proton f,3.89 ppm (singlet, 3H); proton g, 3.55 ppm (quartet, J=7.3 Hz, 1H);proton h, 1.51 ppm (doublet, J=7.3 Hz, 3 H); proton I, 1.25 ppm(triplet, J=7.2 Hz, 3H).

Carbon a, 171.4 ppm, carbon b, 158.7 ppm, carbon c, 165.3 ppm; carbon d,103.6 ppm; carbon e, 141.6 ppm; carbon f, 103.1 ppm; carbon g, 163.1ppm; carbon h, 98.6 ppm; carbon I, 100.1 ppm, carbon j, 156.1 ppm;carbon k, 61.3 ppm; carbon 1, 55.5 or 56.2 ppm; carbon m, 55.5 or 56.2ppm; carbon n, 43.6 ppm; carbon o, 15.0 ppm; carbon p, 14.0 ppm.

An oven dried 25-mL 3-neck round bottomed flask, equipped with anitrogen inlet, magnetic stirring bar, and rubber septum, was chargedwith acetonitrile (5.0 mL) and 1,8-diazabicyclo[5.4.0]-undec-7-ene(“DBU”) (0.3 mL) with stirring. 6,8-Dimethoxy-isochroman-1,3-dione (25)(222.2mg) dissolved in acetonitrile (5.0 mL) was added to the stirringsolution by syringe pump over a 48 minute period at ambient temperature.The acid chloride of formula (28) (246.9 mg) was added by syringe over 4minutes and then stirred an additional 10 minutes. An in-process controlsample showed 96.5% conversion to the isocoumarin (2) as measured byreverse-phase BPLC using a C18, 5μ column (Phenomenex Luma) and a mobilephase of 1:1 acetonitrile-water. An additional 5 drops of the acidchloride (27) was added and the solution stirred for 10 minutes.Analysis of an in-process control sample indicated 96.6% conversion. Thereaction was stirred for 17 hrs at ambient temperature resulting in a99.9% conversion.

The solution was stripped of solvent to yield a reddish-brown oil thatwas then dissolved in 10 mL ethyl acetate and 10 mL of 1.0 N HCl. Thelayers were split and the organic layer was washed with 5 mL of 1.0 NHCl. The combined acidic layers were back-extracted with 5 mL ethylacetate. The combined organic extracts were combined and washed twicewith saturated NaHCO₃ and once with saturated NaCl. The solution wasdried over MgSO₄ and the solvent removed in vacuo to give 240.3 mg of2-(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-propionic acid ethyl ester(2) as an orange oil (purity 89.9% a.u.c).

An oven dried 25 mL 3-neck flask, equipped with a nitrogen inlet,magnetic stir bar, and a rubber septum, was charged with 10 mLacetonitrile and TMG (29) with stirring. The solution was cooled to −20°C. and (25) in acetonitrile (6 mL) was added over 24 minutes via syringepump maintaining an internal temperature of −20° C. TEA (0.28mL) wasadded in one portion. The acid chloride (28) was added by syringe over 3minutes and then stirred an additional 20 minutes. The cooling bath wasremoved and the reaction allowed to warm to ambient temperature and thenstirred approximately 18 hours at ambient temperature. The reaction waspoured into 0.1N HCl (25 mL) and ethyl acetate (25 mL) and the phaseswere separated. The organic layer was washed twice with saturated NaHCO₃(25 mL) and the combined aqueous layers were back-extracted with ethylacetate (10 mL). The organic layers were washed with brine (25 mL) andthen dried over MgSO₄ prior to removal of the solvent in vacuo to givethe isocoumarin (2) (242 mg, 79% yield) as an orange oil (purity 95.7%a.u.c.).

Example 2 (6,8-Dimethoxy-1-oxo-1H-isochromen-3-yl)-acetic Acid EthylEster (31)

An oven dried 25-mL 3-neck round bottomed flask, equipped with anitrogen inlet, magnetic stirring bar, and rubber septum, was chargedwith acetonitrile (5.0 mL) and 1,8-diazabicyclo[5.4.0]-undec-7-ene(“DBU”) (0.3 mL) with stirring. 6,8-Dimethoxy-isochroman-1,3-dione (25)(222.19 mg) dissolved in acetonitrile (5.0 mL) was added to the stirringsolution by syringe pump over a 54 minute period at ambient temperature.The acid chloride of formula (30) (0.19 mL) was added by syringe over 5minutes and then stirred an additional 7 minutes. An in-process controlsample showed 85% conversion to the isocoumarin (31) as measured byreverse-phase HPLC using a C18, 51μ column (Phenomenex Luma) and amobile phase of 1:1 acetonitrile-water. An additional 68 minutes ofstirring resulted in an increase to 87% conversion. An additional amountof the acid chloride (30) (30 μl) was added and the solution stirredovernight at ambient temperature resulting in a 94% conversion.Additional DBU was added (70 μl) and stirred for 2.6 hr resulting in 99%conversion.

The solution was diluted with 20 mL of ethyl acetate and washed with 20mL of water. Toluene was added to the organic fraction and azodried. Asolid formed which was slurried in CDCL₃ and then filtered throughNa₂SO₄ and cotton. Solvent was removed to afford 246.8 mg of(6,8-dimethoxy-1-oxo-1H-isochromen-3-yl)-acetic acid ethyl ester (31) asan orange oil which solidified upon standing (purity 84.5% a.u.c.).Designations assigned to NMR analysis of the isocoumarin of formula (31)are as follows:

Proton a, 6.46 ppm (doublet, J=2.3 Hz, 1H); proton b, 6.36 ppm (doublet,J=2.3 Hz, 1H); proton c, 6.30 ppm (singlet, 2H); proton d, 4.20 ppm(quartet, J=7.2 Hz, 2H); proton e, 3.96 ppm (singlet, 3 H); proton f,3.89 ppm (singlet, 3H); proton g, 3.55 ppm (quartet, J=7.3 Hz, 1H);proton h, 1.27 ppm (triplet, J=7.2 Hz, 3H).

Example 3 2-(6,8-Dimethoxy-1-oxo-1H-isochromen-3-yl)-cyanomethane (32)

An oven dried, 25 mL, 3 neck flask, equipped with a magnetic stir barunder N₂ purge was charged with 0.474 g of cyanoacetic acid (AcrosOrganics) (33) at ambient temperature. Acetonitrile (“MeCN,” Aldrich,Milwaukee, Wis.), 10 mL, was added to give a clear solution to whichcarbonyl diimidazole (“CDI,” Aldrich, Milwaukee, Wis.), 0.908 g in 10 mLacetonitrile, was added. Triethylamine (“TEA,” Aldrich, Milwaukee,Wis.), 0.78 mL, was added to the solution over 30 sec.6,8-Dimethoxy-isochroman-1,3-dione (25), 0.629 g in 10 ml acetonitrile,was added via syringe over 11 minutes at ambient temperature. Thereaction mixture was stirred at ambient temperature for approximately 22hours and the solvent removed from the mixture producing a yellow solid.The solid was partitioned between ethyl acetate (50 mL) and 0.5N HCl (40mL) and the organic phase was washed first with water (40 mL) and thentwice with ½saturated NaHCO₃ (40 mL). The ethylacetate phase was driedover MgSO₄ (5.4 gm) followed by solvent removal and titration underisopropyl alcohol:ethyl acetate (2:1 v/v, 6mL) which gave a pale yellowsolid (70 mg). The acidic aqueous phase form the partitioning wasextracted with dicholormethane (50 mL) with vigorous stirring and thendried over MgSO₄ (4.4 gm) and filtered. Solvent removal and titrationunder isopropyl alcohol:ethylacetate (2:1 v/v, 6 mL) afforded a paleyellow solid (244 mg). HPLC analysis of the yellow solid byreverse-phase HPLC using a C18 5μ column (Phenomenex) and a mobile phaseof 60% acetonitrile in water at a flow rate of 1 ml/min gave a peak at5.1 minutes (90% a.u.c.) and NMR analysis gave the correct spectrum forthe isocoumarin (32).

Example 4 Preparation of Further Isocoumarin Derivatives

The isocoumarin derivatives exemplified in TABLE 2 were prepared asaccording to the instant invention:

wherein the preparation proceeded by: (A) addition of the anhydride (3)into a solution containing the activated carboxylic acid (4) and base;or (B) addition of anhydride (3) into base via syringe followed byaddition of activated carboxylic acid (4). A standard work-up procedureconsisted of a 1N HCl wash to remove the base, a saturated NaHCO₃ washto remove any dimerized byproduct, and a saturated NaCl wash to removewater from the organic phase, followed by NaSO₄ drying and stripping ofthe solvent.

TABLE 2 Product Compound (3) Proc. Base Time Temp. % Yield

A TEA 5 hr 50° C. 73

A TEA 2.3 hr   50° C. 76

A TEA 5 hr 50° C. 91

A TEA 5 hr 50° C. Inc.^(†)

B TMG 1 hr  0° C. 51 ^(†)reaction not run to completion within reactiontime.

In addition, diketene,

was used instead of a compound of formula (4) to react with6,8-dimethoxy-isochroman-1,3-dione (25) to produce the isocoumarin offormula (38):

Self condensation products were also identified in the above reactions.Thus, in addition to previously described self-condensation product, theanhydrides:

give rise respectively to the self-condensation products:

In addition to the forgoing, additional exemplifications of the R³ groupof the activated carbonyl compound (4) include, but are not limited to,—CONH₂, —SOCH₃, —NO₂, —NC, and —N═C—C₆H₆. Additional exemplifications ofthe activated carbonyl compound (4) include, but are not limited to:

wherein the product isocoumarin derivatives are respectively:

and R¹, Y and X_(n) are as previously defined and p is an integer from 1to 4.

The isocoumarin derivatives produced by the methods of the instantinvention may also serve as substrates for the preparation of otherisocoumarin analogs. E.g., wherein the activated carbonyl compound is:

the resulting isocoumarin derivative is:

The compound (49) is used as a substrate in the formation of furtherisocoumarin analogs:

Example 5 Preparation of 2-Carboxymethyl-4,6-dimethoxybenzoic Acid A.Synthesis of Diethylester Intermediate

An oven dried 250 mL 3-neck round bottomed flask, equipped with anitrogen inlet, magnetic stir bar, thermocouple and rubber septa, wascharged with NaH (0.8 gm) and 50 mL dry tetrahydrofuran (THF). Thissuspension was stirred at ambient temperature and diethylmalonate (54)was added over 5 minutes dropwise via syringe.1-Bromo-2,4-dimethoxybenzene (55) (1.08 g), was added in one portion viasyringe to the stirring solution. The flask was then cooled to below−20° C. by an ethanol/H₂O/CO₂ bath. To a separate oven dried 100 ml3-necked round bottomed flask, equipped with a rubber septa, magneticstir bar and nitrogen inlet, was charged a few crystals of1,10-phenanthroline as indicator and 25 mL dry THF. The flask was cooledto below −60° C. A few drops of n-butyl lithium were added until thebrown color of the indicator persisted. The n-butyl lithium (3.05 mL)required for formation of the lithium diisopropylamide (LDA) was thenadded, followed by slow addition of diisopropylamine (0.91 mL). Thissolution was stirred for 20 minutes. The LDA was then added dropwise viacannula over 24 minutes maintaining a temperature between −20 and −30°C. Over 2 hours, 2.5 mL (1 eq) of an estimated 2M solution of LDA wasadded until an in-process control sample indicated greater than 97%conversion. The reaction was quenched at low temperature with 20 mL of1.0N HCl solution prior to warming to ambient temperature. The solutionwas acidified with 1.0N HCl and the two phases separated. The organicfraction was washed with 25 mL 1.0N HCl and then saturated NaCl. Thesolution was filtered through a plug of MgSO₄. After removal of solventin vacuo, 2.65 g of 2-carboxymethyl-4,6-dimethoxybenzoic acid diethylester (56) as a yellow/orange oil (purity 93.2% a.u.c) was obtained.Designations assigned to NMR analysis of the compound of formula (56)are as follows:

Proton a, 6.40 ppm, (apparent singlet, 2H); proton b, 4.34 ppm (quartet,J=7.2 Hz, 2H); proton c, 4.14 ppm (quartet, J=7.2 Hz, 2H); proton d,3.817 ppm (singlet, 3H); proton e, 3.811 ppm (singlet, 3H); proton f,3.66 ppm (singlet, 2H); proton g, 1.35 ppm (triplet, J=7.2 Hz, 3H);proton h, 1.24 ppm (triplet, J=7.2 Hz, 3H).

Carbon a, 170.6 ppm; carbon b, 161.4 ppm; carbon c, 167.1 ppm; carbon d,107.3 ppm; carbon e, 134.8 ppm; carbon f, 116.2 ppm; carbon g, 158.8ppm; carbon h, 97.7 ppm; carbon I, 60.8 OR 60.77 PPM; carbon j, 60.8 or60.77 ppm; carbon k, 55.8 ppm; carbon 1, 55.2 ppm; carbon m, 39.5 ppm;carbon n, 14.0 ppm.

Step 1: Preparation of 1-chloro-2,4-dimethoxybenzene (58):

A 30 L, multi-neck jacketed flask, equipped with a thermocouple,mechanical stirrer, nitrogen purge and peristaltic pump was charged with4-chlororesorcinol (57) (1.4 kg) and water (4.94 kg). The jackettemperature was set at 20° C. and the reactor was charged with 50% NaOH(1.8 kg) keeping the temperature below 35° C. The reactor was thencharged with tert-butyl methyl ether (“TMBE”) (5.85 kg) and a nitrogenpurge was started through the reactor. The reactor was charged withdimethylsulfate (2.66 kg) and the mixture stirred for approximately 18hours at ambient temperature. Stirring was stopped and the layersallowed to separate and the aqueous layer was drained from the reactor.Stirring was started and the reactor charged with water (6.68 kg) and 2%ammonium hydroxide (0.76 kg) and the stirring was then stopped andlayers allowed to separate. The aqueous layer was drained from thereactor. The TMBE was removed by rotary evaporation, the residuedissolved in heptane (2.7 kg) and the vacuum filtered through silica geland solvent removed by rotary evaporation. The residue was distilled toremove heptane to give 1-chloro-2,4-dimethoxybenzene (58) as a paleyellow oil.

Step 2: Preparation of 2-carboxymethyl-4,6-dimethoxybenzoic Acid DiethylEster (56):

An oven dried 1 L 3-neck round bottom flask, equipped with a nitrogeninlet, magnetic stir bar, and rubber septa, was charged with sodiumhydride and THF with stirring. Flask was cooled by EtOH/H₂O/CO₂ bath to˜0° C. and to this stirring slurry was added via syringe pumpdiethylmalonate (54) (23.01 gm) over 40 minutes. To this clear stirringsolution was added 1-chloro-2,4-dimethoxybenzene (58) (42.6 gm) over 5minutes. The flask was cooled to below −20° C. by addition of more dryice to the bath. Lithium diisopropylamide (“LDA”) (2M, 100 mL) was addedvia syringe pump over 67 minutes maintaining an internal temperature of−28 to −20° C. The reaction mixture was stirred for 45 minutes. The dryice bath was removed and the water (200 mL) was added slowly to thestirring solution. The reaction was then allowed to warm to ambienttemperature. The flask contents were transferred to a separatory funneland the lower aqueous phase was drained. The organic layer was washedwith water (2×100 mL). The combined aqueous layers were back extractedwith MTBE (100 mL). The combined organic layers were collected andwashed with 1 N HCl (2×150 mL), water (100 mL) and brine (100 mL). Theorganic layer was dried by stirring overnight with MgSO₄. The dryingagent was filtered off and the solvent was removed in vacuo to give44.67 g. An oily liquid separated which was presumed to be the mineraloil from the sodium hydride dispersion. The crude product was dilutedwith MTBE (500 mL) and stirred with 25 g of Darco and 25 g of basicalumina for 2 hours. The mixture was filtered through Celite to give alight yellow colored solution. The filter cake was washed with MTBE andthe solvent removed in vacuo to give 37.62 g of2-carboxymethyl-4,6-dimethoxybenzoic acid diethyl ester (56) as an oil(purity 97.4% a.u.c).

A 100 mL flask, equipped with a magnetic stirbar, thermocouple, andnitrogen inlet, was charged with sodium hydride (1.12 g, 28.00 mmol) andTHF (10 mL). The mixture was cooled in an ice/water bath. A solution of(59) (0.82 g, 4.746 mmol) in THF (1.5 mL) was added. The vial andsyringe were rinsed with THF (1.0 mL). Diethyl malonate (54) (3.04 g,18.98 mmol) was added over 6 min, keeping the temperature below 5° C.The vial and syringe were rinsed with THF (1.0 mL). Lithiumdiisopropylamide (2.8 mL, 5.6 mmol, 2.0 M) was added to the mixture over1 h, keeping the temp below 5° C. An in-process check by HPLC showed thereaction to be complete. The reaction was quenched with 1.0 N HCl (35mL). The layers were separated and the aqueous layer was extracted twicewith MTBE. The organic extracts were combined and the volatiles wereremoved by rotary evaporation. The residue was dissolved in methanol (20mL) and 50% sodium hydroxide in water (2.0 mL, 37.88 mmol) was added.The mixture was stirred overnight at ambient temperature. An in-processcheck by HPLC showed the reaction to be complete. The mixture wasfiltered. The flask and solids were washed with methanol (10 mL). Thesolids were discarded. The filtrate was reduced by rotary evaporation.The residue was dissolved in water (25 mL) and the resulting aqueoussolution was washed twice with MTBE. The organic layers were discardedand the aqueous layer was acidified with conc HCl until pH<2. Theaqueous layer was extracted twice with ethyl acetate. The organicportions were combined and washed with brine. The volatiles were removedby rotary evaporation to give a tan powder. The ¹H NMR of this materialwas identical to an authentic sample of compound (56).

B. Formation and Isolation of 2-Carboxymethyl-4,6-dimethoxybenzoic Acid(60)

A 2-necked 250 mL round bottomed flask equipped with a stir bar and areflux condenser was charged with the diethyl ester of formula (56)(2.65 gm) and ethanol (100 mL). As the solution was stirred, 10 ml of10% NaOH was added dropwise. The solution darkened and was stirred atambient temperature for 105 min. Analysis of an in-process control (IPC)sample revealed 86.7% conversion to the monoester. After heating thesolution at reflux 3.5 hrs, only 10.3% conversion into the diacid (60)was observed. Conversion was monitored by reverse phase HPLC with a C185μ column and a mobile phase of 60% acetonitrile in water. NaOH as a 10%solution (20 mL) was added. After 1 additional hour of reflux, analysisof an IPC sample revealed 28.6% conversion to the diacid (60). Afterstirring overnight at ambient temperature, no further reaction wasobserved. The solution contained fine suspended solids. The solution washeated to reflux and 20% lithium hydroxide solution (12 mL) was addedand the solution clarified. After 15 minutes, analysis of an IPC samplerevealed 67.2% conversion. Solid NaOH (3 g) was added and stirred for4.75 hours resulting in a 94.8% conversion to the diacid (60).

The solvent volume was reduced in vacuo resulting in a reddish solutionwith particulate matter. The aqueous solution was washed twice with 25mL ethyl acetate to remove non-acidic byproducts. The organic phaseswere extracted with 25 mL of saturated NaHCO₃. The combined alkalineaqueous solutions were placed in a clean 250 mL round bottomed flask andacidified slowly with 12N HCl to an endpoint of pH 1 as determined by pHpaper. The solution was extracted with ethyl acetate (2×50 mL, 1×25 mL)and the organic layers were combined and washed with 25 mL saturatedNaCl solution, dried by passing through a plug of MgSO₄, and stripped ofsolvent to give 2-carboxymethyl-4,6-dimethoxybenzoic acid (60) as anorange solid (0.90 g, purity 88.3% a.u.c.). Designations assigned to NMRanalysis of the compound of formula (60) are as follows:

Proton a, 6.63 ppm (apparent singlet, 2H); proton b, 3.83 ppm (singlet,3H); proton c, 3.77 ppm (singlet, 3H); proton d, 3.73 ppm (singlet, 2H).

Carbon a, 173.4 ppm; carbon b, 168.8 ppm; carbon c, 162.2 ppm; carbon d,108.8 ppm; carbon e, 137.7 ppm; carbon f, 113.7 ppm; carbon g, 159.4ppm, carbon h, 97.7 ppm; carbon I, 56.1 or 55.3 ppm; carbon j, 56.1 or55.3 ppm; carbon k, 40.6 ppm.

A 1 L 3-neck RB flask, equipped with a magnetic stir bar, thermocouple,heating mantle, reflux condenser, and rubber septa with 18 ga. needlefor pressure release, was charged with (56) and methanol and stirreduntil homogeneous. While at ambient temperature, 20% sodium hydroxide(231 mL) was added raising internal temperature to approximately 56° C.The heating mantle was set to 80° C. and the solution became yellow anda solid formed at 38 minutes of reflux. The reaction was held at refluxfor a total of 2.25 hours when the reaction was cooled to ambienttemperature and isopropyl alcohol (100 mL) was added to the slurry andstirred for 15 minutes. The solid product was filtered and the cakewashed with isopropyl alcohol until the filtrate ran colorless.

The solid was dissolved in deionized water (250 mL) and filtered toremove insoluble solids. The basic aqueous solution was charged to aflask and acidified with 12N HCl (10 mL). The product crystallized outof solution and was filtered through a fritted glass funnel. The filtercake was rinsed with deionized water and MTBE. The product dried onfunnel with nitrogen blanketing for 15 minutes, collected and driedunder vacuum at 50° C. overnight. The collected filtrates were strippedof solvent and then acidified with 12N HCl. The product crashed out ofsolution as flakes. Ethyl acetate was added to dissolve most of thesolids, filtered and the phases were separated whereupon the organicphase was washed with brine and dried over MgSO₄ for 1 hour. Severalgrams of Darco were then added and stirred for 15 minutes then filtered.The solvent was removed and then placed on the high vacuum for severalminutes. Crude (60) (4.26 g) was collected (54.1% pure). The solid wasslurried in a small amount of ethyl acetate and then filtered and driedto give 2.42 g of slightly off-white crystals with a purity of 74.5%.

Example 6 Preparation of 6,8-Dimethoxyisochroman-1,3-dione (25)

2-Carboxymethyl-4,6-dimethoxybenzoic acid (60) (3.97 gm) was stirred intoluene (40.0 mL) at ambient temperature in a 100 mL flask with magneticstirring. Acetic anhydride (1.72 mL) was added and the mixture heated to110° C. Monitoring by HPLC revealed that the reaction was completewithin 2.5 hours. Heat was then removed. Crystallization of6,8-dimethoxyisochroman-1,3-dione (25) occurred as the solution cooled.The mixture was cooled to 2° C. After a short hold time, yellowcrystalline solids were filtered, washed with fresh toluene and thendried on high vacuum. 6,8-Dimethoxyisochroman-1,3-dione (25) (3.05 g)was isolated as a yellow crystalline solid.

Example 7 Preparation of 2-Carboxymethyl-3,5-Dimethoxy-Benzoic AcidDiethyl Ester (61)

A summary of the overall synthesis of 2-carboxymethyl-3,5-dimethoxybenzoic acid (61) is shown in FIG. 3. The first step is the synthesis of3,5-dimethoxy-N,N-diethylbenzamide (64). 3,5-Dimethoxy benzoic acid (62)(10.0 g, Acros Organics) and dichloroethane (105 ml) were added to anoven dried 250 ml 3-neck round-bottom flask, equipped with a nitrogeninlet, magnetic stir bar, thermocouple and rubber septum. The mixturewas stirred at ambient temperature and carbonyldiiumidazole (63) (9.79g) was added in one portion. Diethylamine (6.25 ml) was charged in thereactor followed by acetic acid (3.3 ml). The reaction was set to reflux(75° C.) for 2¼ hours. The reaction cooled and more carbonyldiimidazole(63) (8.9 g) was added and stirred at ambient temperature for 16 hr. Anadditional amount of diethylamine (5 ml) was added and the reaction waswarmed to 50° C. and stirred for 22 hr. Additional carbonyldiimidazole(63) and diethylamine were added over 2 days at 50° C. until there was a97% conversion to 3,5-dimethoxy-N,N-diethylbenzamide (64). The productwas isolated was washing the organic layer with 1N HCl then drying andevaporating the organic layer in vacuo to produce as dark peach liquidthat on purification by silica gel chromatography (50:50 ethylacetate/heptane) yielded 13.83 g of (64) as a pale yellow oil (purity92.7% a.u.c.).

The second step is the production of 2-allyl-N,N-3,5-dimethoxy-benzamide(65). A catalytic amount of 1,10-phenanthroline as indicator and TBF (20ml) were charged in a 3-neck 100 ml round-bottom flask equipped with astir bar. The reactor was cooled to −70° C. under nitrogen purge.Freshly titrated s-BuLi (10.5 ml) was charged dropwise until apurple/brown color persisted, then the full charge of base was added.Amide (64) (2.0 g) was dissolved in THF and slowly added to the s-BuLisolution over 30 min. Copper bromide dimethylsulfide complex (2.53 g)was charged as a single portion and the reaction stirred for 5 min.Allyl bromide (0.88 ml) was charged to the reactor over 10 min and thenstirred for an additional 70 min. An in-process control showed an 85.9%conversion to (65). The reaction was poured into 50 ml of 1N HCl and theproduct was extracted with ethyl acetate twice and the organic layerswashed with 50 ml water. An insoluble solid formed and was filtered out.The organic layer was separated and washed with saturated NaCl and thendried over MgSO₄. The drying agent was filtered off and solvent removedin vacuo to give the crude product as a brown oil. Purification bysilica gel chromatography (20:80 ethyl acetate/heptane) yielded 1.0 g of(65) as an oil (purity 87.9 a.u.c.).

The third step is preparation of(2-diethylcarboxamoyl-4,6-dimethoxy-phenyl)-acetic acid (66). Compound(65) (0.92 g), acetonitrile (19.8 ml), water (12.6 ml) and CCl₄ (12.6ml) were charged to a 3-necked 50 ml round-bottom flask. RuCl₃ (0.69 g)and Sodium periodate (4.73 g) was charged in three portions over 3.5 hrand stirred vigorously. The reaction completed in 3 hr wherein themixture was filtered through Celite and the cake rinsed with ethylacetate (25 ml). The filtrate was charged to a separatory funnel and thephases were split. The organic layer was washed with water (15 ml). Theaqueous layers were combined and extracted with ethyl acetate (15 ml).The combined organic layers were dried over magnesium sulfate andremoved in vacuo to yield 0.88 g crude product. Crude (66) was purifiedby preparative HPLC (50% water/acetonitrile) to afford 241 mg of (66)(97.2% a.u.c.).

The fourth step is preparation of 2-carboxymethyl-3,5-dimethoxy-benzoicacid (67). Compound (66) (0.130 g), water (2 ml) and 12 N HCl (2 ml)were charged to a screw-cap tube. The tube was stirred and heated toreflux for 2.5 hr. Upon cooling a solid formed. The solid was dissolvedin ethyl acetate and aqueous layer was extracted twice with ethylacetate. The combined organic layers were washed with 1N HCl and brine,then dried over magnesium sulfate and solvent removed in vacuo to give85.5 mg of (67) as a tan solid (94.8 a.u.c.).

In the final step, compound (67) (85.5 mg) and ethanol (5 ml) werecharged to an oven dried round bottom flask. A catalytic amount ofdimethylformamide (1 drop) was charged followed by thionyl chloride(0.26 ml). The reaction was stirred overnight and the solvent thenremoved in vacuo. The reaction was taken into dichloromethane (1 ml) andcarbonyldilmidazole (63) (65 mg) was charged in a single portion andstirred for 25 min. Anhydrous ethanol (5 ml) was added and stirredovernight. Additional carbonyldiimidazole (63) was charged, followed bymore ethanol and the reaction stirred for 2 hr. The solvent was removedfrom the reaction and the residue was taken into ethyl acetate. Theorganic phase was washed twice with 1N HCl and brine. The organic layerwas dried over magnesium sulfate and solvent removed in vacuo. The crudeproduct was purified by preparative TLC (49.9:49.9:0.2 ethylacetate/heptane/acetic acid) to give 8.5 ml of (61) as a tan oil (94.8%a.u.c.).

Example 8 Regioselectivity of Homophthalate Ester Formation

The amount of regioisomeric homophthalate ester being produced wasverified by analysis of crude benzyne reaction mixtures of a1-halo-2,4-dimethoxybenzene and dimethylmalonate. HPLC analysis. Sampleswere analyzed by reverse-phase HPLC using a C18 5μ column and a mobilephase of 1:lacetonitrile and water. Quantification was by calculation ofpeak area of UV detection at 210 to 300 nm. Using photo diode array forpeak identity comparison, no 2-carboxymethyl-3,5-dimethoxy-benzoic aciddiethyl ester (61) could be detected. Thus, based on this level ofdetection, the reaction of the halobenzene (58) with diethylmalonateproduces a single product isomer 2-carboxymethyl-4,6-dimethoxy-benzoicacid diethyl ester (56).

The present invention has been shown by both description and examples.The Examples are only examples and cannot be construed to limit thescope of the invention. One of ordinary skill in the art will envisionequivalents to the inventive process described by the following claimsthat are within the scope and spirit of the claimed invention.

What is claimed is:
 1. A process for the preparation of isocoumarinderivatives of the formula

wherein R¹ and R² are independently H, halogen, C₁-C₆ alkyl, C₁-C₆alkenyl, C₁-C₆ alkynyl, aryl, heteroaryl, C₁-C₆ acyl, C₁-C₆ alkoxyl,—NR⁴R⁵, wherein when R⁴ is H then R⁵ is sulphonyl or C₁-C₆ acyl or whereR⁴ and R⁵ are independently C₁-C₆ alkyl or C₁-C₆ acyl; and R³ is anelectron withdrawing group; X is a substituent selected from halo, C₁-C₆alkyl, C₁-C₆ alkenyl, C₁-C₆ alkynyl, aryl, heteroaryl, C₁-C₆ acyl, C₁-C₆alkoxyl, —NR⁴ R⁵, wherein R⁵ and R⁴ are as defined above, or SO₂R⁶,where R⁶ is C₁-C₆ alkyl or C₁-C₆ acyl; and n is an integer from 0 to 4,wherein when n is greater than 1 the X substituents may be the same ordifferent; comprising reacting a homophthalic anhydride of the formula

wherein R¹, X and n are as defined above; with a carbonyl compound ofthe formula

wherein R² and R³ are as defined above; and Y is an acyl activatingsubstituent; in the presence of a reaction medium comprising a solventand a base.
 2. The process of claim 1, wherein R³ is an electronwithdrawing group selected from the group consisting of aryl, hetroaryl,sulfonate, phosphonate, cyano, —CO₂R⁷, wherein R⁷ is C₁-C₆ alkyl, and—COR⁸, wherein R⁸ is a halogen.
 3. The process of claim 1, wherein R³ is—CO₂C₂H₅.
 4. The process of claim 1, wherein X is —OCH₃.
 5. The processof claim 4, wherein n is
 2. 6. The process of claim 1, wherein Y is anacyl activating substituent selected from the group consisting ofhalogen, imidazoyl, pyridyl and aryloxy.
 7. The process of claim 6,wherein said halogen is chloro, bromo or iodo.
 8. The process of claim1, wherein Y is imidazoyl.
 9. The process of claim 1, wherein saidsolvent is an aprotic solvent.
 10. The process of claim 9, wherein saidaprotic solvent is a halogenated or ethereal solvent.
 11. The process ofclaim 9 wherein said aprotic solvent is acetonitrile or N-methylpyrrolidinone.
 12. The process of claim 1, wherein said base is selectedfrom the group consisting of tertiary amine, amidine, amide and tertiaryalkoxide bases.
 13. The process of claim 1, wherein said base istriethylamine.
 14. The process of claim 1, wherein said base is1,8-diazabicylco[5.4.0]-undec-7-ene.
 15. A process for the preparationof isocoumarin derivatives of the formula:

wherein R¹¹ and R¹² are independently C₁-C₆ alkyl; and R⁹ and R¹⁰ areindependently C₁-C₆ alkyl or C₁-C₆ alkoxy; comprising reacting ahomophthalic anhydride of the formula:

wherein R⁹ and R¹⁰ are as defined above; with a carbonyl compound of theformula:

wherein R¹¹ and R¹² are as defined above; and Y is an acyl activatinggroup; in the presence of a reaction medium comprising a solvent and abase.
 16. The process of claim 15, wherein Y is an acyl activating groupselected from the group consisting of halogen, imidazoyl, pyridyl andaryloxy.
 17. The process of claim 16, wherein said halogen is chloro,bromo or iodo.
 18. The process of claim 15, wherein Y is imidazoyl. 19.The process of claim 15, wherein said solvent is an aprotic solvent. 20.The process of claim 19, wherein said aprotic solvent is a halogenatedor ethereal solvent.
 21. The process of claim 19, wherein said aproticsolvent is acetonitrile or N-methyl pyrrolidinone.
 22. The process ofclaim 15, wherein said base is selected from the group consisting oftertiary amine, amidine, amide and tertiary alkoxide bases.
 23. Theprocess of claim 15, wherein said base if triethylamine.
 24. The processof claim 15, wherein said base is 1,8-diazabicylco[5.4.0]-undec-7-ene.25. The process of claim 15, wherein R¹¹ is methyl, R¹² is ethyl, and R⁹and R¹⁰ are methoxy and said isocoumarin derivative is:


26. The process of claim 25, further comprising removal of the ethylester group and a methyl group from said isocoumarin derivative:

to provide the isocoumarin derivative of the formula: